The present invention is directed to trenching techniques for conductive electronic interconnects, and more particularly to methods for fabricating channels and vias in high density multilayers such as substrates and integrated circuits in few and simple steps.
High density copper/polyimide interconnects can be fabricated by providing conductors on a base, building interlayer pillars on the conductors, and coating the conductor-pillar structure with polyimide. This has several drawbacks: the metal conductor-pillar structure is vulnerable to mechanical damage before polyimide encapsulation; resist scumming can develop on underlying patterned layers after wet chemical etching; particles on the surface prior to plating can plate up quickly causing interlayer short circuits; and cooling after the 400.degree. C. polyimide cure can create stress between the copper and polyimide since copper has a greater thermal coefficient of expansion.
These drawbacks associated with conductor-pillar structures can be overcome by forming trenches for vias and channels in a polyimide layer and then filling the trenches with a conductor. One such method for fabricating high density electronic circuits having narrow conductors is disclosed by Becker in U.S. Pat. No. 4,417,393. There are several drawbacks to Becker's method, including the need for two insulating layers with different depths to form vias and conductors in an insulating layer, the need for laser machining, and the inability to incorporate electrodeposition.
Furthermore, current interconnect fabrication methods with relatively few steps form conductive channels and vias simultaneously but fail to provide via stacking. Alternative methods which provide via stacking require a relatively large number of process steps.